Probing the Thermal Implications in Mechanical Degradation of Lithium-Ion Battery Electrodes

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Capacity fade in lithium-ion batteries remains an area of active research, with failure of the graphite anode thought to be an important contributor. While the formation of the solid electrolyte interphase and the subsequent loss of cyclable lithium have been well studied, mechanical degradation remains an area where ambiguity remains. While there appears to be little experimental evidence that suggest that macroscopic particle cracking occurs, mathematical models have suggested that this phenomenon is likely. The goal of this paper is to clarify this ambiguity by combining experimental cycling, mathematical stress modeling, and post-mortem microscopy. We experimentally determine an average diffusion coefficient of lithium in graphite using a thin-layer electrode and use this information in a diffusion-induced stress model. Our results suggest that cracking is not likely during lithiation due to the proximity of equilibrium potential to the cutoff potential. On delithiation, at 25 • C, even at 30 C rate cracking is unlikely while at −10 • C, a rate of 10 C can lead to particle cracking. By extrapolating the results of the thin-layer electrode to a thick porous electrode, we found that graphite cracking is unlikely to occur during typical vehicle operations. In recent years, there have been numerous studies on lithium-ion batteries for vehicle applications. [1][2][3][4][5] Of particular interest are the various degradation mechanisms encountered when operating the battery under severe conditions (i.e., wide temperature ranges and high Crates) typical for vehicle applications.6 One likely degradation mechanism is the mechanical breakdown of the active materials. Lithium insertion (or extraction) into (or out of) the lattice of the active materials causes volume change (expansion and contraction), resulting in stress generation and possible fracture of the particles. For example, in graphite anodes, crack generation can expose new surfaces to the electrolyte, leading to further formation of the solid electrolyte interphase (SEI) 7,8 and/or particle isolation from the electronic network, leading to impedance growth, loss of cyclable lithium, and capacity fade.Mathematical models, based on diffusion-induced stress generation, have been used to investigate particle fracture and have suggested that graphite particle cracking is likely under certain conditions. [9][10][11][12][13] For the diffusion-induced stress model, diffusion coefficient in solid phase is a key parameter to determine the concentration gradient in the particle, which in turn affects the stress generated.9 However, there is a wide disparity in the measured diffusion coefficient of lithium in graphite, ranging from 10 −16 to 10 −11 m 2 /s. [14][15][16][17][18][19] This wide range can be attributed to different kinds of graphite used in these studies in addition to different techniques used to extract the diffusion coefficient. Model predictions would suggest that for the lower value of diffusion coefficient (1.0 × 10 −14 m 2 /s) particle cracking durin...

“…However, this trend is balanced by the decreased utilization as particle size increases, resulting is less stress due to the shortened time for stress generation. 13 …”

Section: Resultsmentioning

confidence: 99%

“…[9][10][11][12][13] For the diffusion-induced stress model, diffusion coefficient in solid phase is a key parameter to determine the concentration gradient in the particle, which in turn affects the stress generated. 9 However, there is a wide disparity in the measured diffusion coefficient of lithium in graphite, ranging from 10 −16 to 10 −11 m 2 /s.…”

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confidence: 99%

Examination of Graphite Particle Cracking as a Failure Mode in Lithium-Ion Batteries: A Model-Experimental Study

Takahashi

Srinivasan

2015

109

104

“…The complexity of the approach is in the accurate mapping of the field variables (like concentration) from the spherical grid to the spring network while accounting for large deformation of the spring network. The approach has previously been demonstrated for pristine low volumetric expansion active material like graphite [42][43][44][45][46][47] and high capacity electrode active material particles like silicon and tin with two-phase diffusion. 40,41 In this work, we extend the model to do a comparative analysis of the fracture map for two-phase versus single phase diffusion inside silicon while accounting for the presence of a surface film by adding an additional layer of springs with spring stiffness different from the active material to investigate the resulting change in fracture map.…”

Section: Methodsmentioning

confidence: 99%

Mechanistic Analysis of Mechano-Electrochemical Interaction in Silicon Electrodes with Surface Film

Verma

Mukherjee

2017

Self Cite

High-capacity anode materials for lithium-ion batteries, such as silicon, are prone to large volume change during lithiation/delithiation which may cause particle cracking and disintegration, thereby resulting in severe capacity fade and reduction in cycle life. In this work, a stochastic analysis is presented in order to understand the mechano-electrochemical interaction in silicon active particles along with a surface film during cycling. Amorphous silicon particles exhibiting single-phase lithiation incur lower amount of cracking as compared to crystalline silicon particles exhibiting two-phase lithiation for the same degree of volumetric expansion. Rupture of the brittle surface film is observed for both amorphous and crystalline silicon particles and is attributed to the large volumetric expansion of the silicon active particle with lithiation. The mechanical property of the surface film plays an important role in determining the amount of degradation in the particle/film assembly. A strategy to ameliorate particle cracking in silicon active particles is proposed. Lithium ion battery (LIB) technology has become the prevalent energy storage and supply system for portable electronics.1 In recent years, the application of LIBs is extending to large scale applications such as electric vehicles, 2-4 commercial aircrafts 5,6 and grid energy storage. 7,8 The widespread usage of LIBs in high energy and power applications is predicated on robust improvement of energy and power densities afforded by the LIB which is directly correlated with the anode 9,10 and cathode 11,12 active materials utilized. Current commercial batteries use graphite 13 as anode and lithium cobalt oxide/lithium nickel manganese cobalt oxide 14,15 as cathode material. Graphite exhibits a maximum specific capacity of 372 mAh/g graphite while the current cathode materials are limited to a maximum of 200 mAh/g AM . These chemistries have been utilized in electric vehicle batteries, however, the low capacity necessitates use of bulky and expensive battery packs to power the vehicle which form the major impediment to commercialization of electric vehicles.Extensive efforts have been invested in identifying high capacity anode and cathode materials for usage in next generation lithium ion batteries.10 Silicon has been the focus of several researchers as an anode material owing to its high theoretical specific capacity of 4200 mAh/g Si , approximately ten times that of graphite. [16][17][18] This high capacity is a result of large lithium intercalation ability of silicon as compared to graphite; a silicon atom can intercalate a maximum of 4.4 atoms of lithium (Li 4.4 Si) while graphite can accommodate a maximum of 1 lithium atom per graphite molecule (LiC 6 ).17 However, experimental analysis of silicon anode lithium ion battery has revealed much lower capacities (∼75% of the theoretical capacity) during initial cycles 19 as well as rapid capacity degradation with charge-discharge cycling. Capacity fade of the order of 20% is observed within the first...

“…21,46 The effect of ambient temperature on the evolution of diffusion-induced stress revealed that mechanical degradation is prone to occur more in low temperature operations. 47 Experimental characterization of microcrack evolution within active particles can …”

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confidence: 99%

“…Development of a reduced order model.-According to the authors, evolution of microcrack density occurs toward the beginning of the delithiation process. 21,47 Eventually, the amount of microcrack formation reaches a state of saturation, and no further increase in mechanical degradation is observed during subsequent discharge-charge cycles. Thus, an exponential increase in damage evolution followed by saturation can be successfully captured by Eq.…”

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confidence: 99%

Reduced Order Modeling of Mechanical Degradation Induced Performance Decay in Lithium-Ion Battery Porous Electrodes

Barai

Smith

Chen

et al. 2015

Self Cite

A one-dimensional computational framework is developed that can solve for the evolution of voltage and current in a lithium-ion battery electrode under different operating conditions. A reduced order model is specifically constructed to predict the growth of mechanical degradation within the active particles of the carbon anode as a function of particle size and C-rate. Using an effective diffusivity relation, the impact of microcracks on the diffusivity of the active particles has been captured. Reduction in capacity due to formation of microcracks within the negative electrode under different operating conditions (constant current discharge and constant current constant voltage charge) has been investigated. At the beginning of constant current discharge, mechanical damage to electrode particles predominantly occurs near the separator. As the reaction front shifts, mechanical damage spreads across the thickness of the negative electrode and becomes relatively uniform under multiple discharge/charge cycles. Mechanical degradation under different drive cycle conditions has been explored. It is observed that electrodes with larger particle sizes are prone to capacity fade due to microcrack formation. Under drive cycle conditions, small particles close to the separator and large particles close to the current collector can help in reducing the capacity fade due to mechanical degradation. Due to their high energy and power density, lithium-ion batteries (LIBs) are being used extensively in the electrification of the automotive industry through the development of electric and hybrid electric vehicles (EVs and HEVs).1-3 Several mechanisms exist that can cause a reduction in the capacity of LIBs and subsequent loss of life. [4][5][6][7] Growth of a solid electrolyte interface (SEI) layer on the carbon active particles of the anode is the major reason behind the loss of cyclable lithium ions. [8][9][10] Lithium plating at low temperatures also results in loss of lithium and subsequent capacity fade.11 Delamination of the current collector from the electrode due to gas evolution in the electrolyte can significantly increase the internal resistance of the lithium-ion cell. 12 Crack propagation, rupture, and isolation of portions of active particles can also cause loss of active sites where lithium atoms can intercalate, resulting in effective capacity fade. 13 In the past two to three decades, capacity fade due to the formation of SEI 8,10,[14][15][16][17] and lithium plating 18,19 have been investigated thoroughly. On the other hand, resistance growth and capacity fade due to delamination and site loss have not been explored extensively. In the recent past, some research initiatives have focused on characterizing the generation of diffusion-induced stress within the active particles. 20 A computational methodology was developed to capture the formation of cracks based on the material heterogeneity of the anode active particles. 21 In the present article, the authors have developed a comprehensive reduced order model (RO...